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In highly ephemeral freshwater habitats, predatory vertebrates are typically unable to become established, leaving an open niche often filled by macroinvertebrate predators. However, these predators are faced with the challenge of finding sufficient food sources as the rapid rate of desiccation prevents the establishment of extended food chains and limits the number of prey species present. It could therefore be advantageous for predators to synchronize their phenology with that of their prey within sites of extreme ephemerality. We report the first case of adult diving beetles (Hydaticus parallelus) ovipositing their eggs within spawn of an amphibian species (sandpaper frog, Lechriodus fletcheri). This behavior was found among several pools used by L. fletcheri for reproduction. Beetle eggs oviposited in frog spawn were found to hatch within 24 h of the surrounding L. fletcheri eggs, with the larvae becoming voracious consumers of the hatched tadpoles. Although it has yet to be established experimentally whether this is an adaptive behavior, the laying of eggs among potential future tadpole prey in this instance should confer significant fitness benefits for the offspring upon hatching, ensuring that they are provided an immediate source of food at the start of their development and potentially throughout. This oviposition behavior might be common among diving beetles and could form a significant predatory threat for amphibians with a free-swimming larval stage in ephemeral freshwater habitats. [ABSTRACT FROM AUTHOR]

The role of invertebrate predation in shaping vertebrate communities is often overlooked. This is evident with predaceous diving beetles (Coleoptera: Dytiscidae), which are often the top predator in many aquatic freshwater habitats. During weekly monitoring of a reintroduction for an endangered frog, a group of a dozen adult diving beetles were encountered attacking and quickly dismembering and consuming a tadpole. A single adult diving beetle was also discovered burrowing its head inside and consuming a tadpole approximately 3–4 times its size by seemingly piercing its prey to suck out its liquefied remains. This is in contrast with the well known behaviour of adult dytiscids, which involves tearing prey into small pieces with their chewing mouthparts. Although dytiscids are known to occasionally consume vertebrates such as tadpoles, adults are typically considered scavengers, and this communal predatory behaviour and feeding method have not previously been documented. Moreover, over 80% of the tadpoles in the monitored site were found in ponds with no beetles and despite representing only a quarter of all ponds, half of the tadpoles across the landscape were in ponds free of diving beetles, demonstrating a possible influence of diving beetles on tadpoles. These observations may have implications for amphibian conservation since management efforts are not typically concerned with naturally occurring ubiquitous threats such as those from small invertebrate predators, as it has rarely been observed in nature. Although amphibian conservation plans expect some losses from natural predation, diving beetles may affect conservation efforts such as captive breeding and reintroductions with populations where every individual is critical to success. During monitoring of a habitat reintroduction in New South Wales, a group of a dozen adult diving beetles attacked and very quickly dismembered a tadpole. An adult diving beetle was also observed burrowing its head inside and consuming a much larger tadpole. These observations may have implications for amphibian conservation since management efforts are not typically concerned with naturally occurring ubiquitous threats such as those from small invertebrate predators, as they have rarely been observed in nature. Photo by Dr Jose Valdez. [ABSTRACT FROM AUTHOR]